Bit interleaver for low-density parity check codeword having length of 64800 and code rate of 7/15 and quadrature phase shift keying, and bit interleaving method using same

ABSTRACT

A bit interleaver, a bit-interleaved coded modulation (BICM) device and a bit interleaving method are disclosed herein. The bit interleaver includes a first memory, a processor, and a second memory. The first memory stores a low-density parity check (LDPC) codeword having a length of 64800 and a code rate of 7/15. The processor generates an interleaved codeword by interleaving the LDPC codeword on a bit group basis. The size of the bit group corresponds to a parallel factor of the LDPC codeword. The second memory provides the interleaved codeword to a modulator for quadrature phase shift keying (QPSK) modulation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/606,949, filed Jan. 27, 2015, which claims the benefit of KoreanPatent Application Nos. 10-2014-0011492 and 10-2015-0002166, filed Jan.29, 2014 and Jan. 7, 2015, respectively, which are hereby incorporatedby reference herein in their entirety.

BACKGROUND

1. Technical Field

The present disclosure relates generally to an interleaver and, moreparticularly, to a bit interleaver that is capable of distributing bursterrors occurring in a digital broadcast channel.

2. Description of the Related Art

Bit-Interleaved Coded Modulation (BICM) is bandwidth-efficienttransmission technology, and is implemented in such a manner that anerror-correction coder, a bit-by-bit interleaver and a high-ordermodulator are combined with one another.

BICM can provide excellent performance using a simple structure becauseit uses a low-density parity check (LDPC) coder or a Turbo coder as theerror-correction coder. Furthermore, BICM can provide high-levelflexibility because it can select modulation order and the length andcode rate of an error correction code in various forms. Due to theseadvantages, BICM has been used in broadcasting standards, such as DVB-T2and DVB-NGH, and has a strong possibility of being used in othernext-generation broadcasting systems.

However, in spite of those advantages, BICM suffers from the rapiddegradation of performance unless burst errors occurring in a channelare appropriately distributed via the bit-by-bit interleaver.Accordingly, the bit-by-bit interleaver used in BICM should be designedto be optimized for the modulation order or the length and code rate ofthe error correction code.

SUMMARY

At least one embodiment of the present invention is directed to theprovision of an intra-BICM bit interleaver that can effectivelydistribute burst errors occurring in a broadcasting system channel.

At least one embodiment of the present invention is directed to theprovision of a bit interleaver that is optimized for an LDPC coderhaving a length of 64800 and a code rate of 7/15 and a quadrature phaseshift keying (QPSK) modulator performing QPSK modulation and, thus, canbe applied to next-generation broadcasting systems, such as ATSC 3.0.

In accordance with an aspect of the present invention, there is provideda bit interleaver, including a first memory configured to store alow-density parity check (LDPC) codeword having a length of 64800 and acode rate of 7/15; a processor configured to generate an interleavedcodeword by interleaving the LDPC codeword on a bit group basis, thesize of the bit group corresponding to a parallel factor of the LDPCcodeword; and a second memory configured to provide the interleavedcodeword to a modulator for QPSK modulation.

The parallel factor may be 360, and each of the bit groups may include360 bits.

The LDPC codeword may be represented by (u₀, u₁, . . . , u_(N) _(ldpc)⁻¹) (where N_(ldpc) is 64800), and may be divided into 180 bit groupseach including 360 bits, as in the following equation:X _(j) ={u _(k)|360×j≤k<360×(j+1), 0≤k<N _(ldpc)} for 0≤j<N _(group)where X_(j) is anj-th bit group, N_(ldpc) is 64800, and N_(group) is180.

The interleaving may be performed using the following equation usingpermutation order:Y _(j) =X _(π(j)) 0≤j≤N _(group)where X_(j) is thej-th bit group, Y_(j) is an interleaved j-th bitgroup, and π(j) is a permutation order for bit group-based interleaving(bit group-unit interleaving).

The permutation order may correspond to an interleaving sequencerepresented by the following equation:interleaving sequence={152 172 113 167 100 163 159 144 114 47 161 125 9989 179 123 149 177 1 132 37 26 16 57 166 81 133 112 33 151 117 83 52 17885 124 143 28 59 130 31 157 170 44 61 102 155 111 153 55 54 176 17 68169 20 104 38 147 7 174 6 90 15 56 120 13 34 48 122 110 154 76 64 75 84162 77 103 156 128 150 87 27 42 3 23 96 171 145 91 24 78 5 69 175 8 29106 137 131 43 93 160 108 164 12 140 71 63 141 109 129 82 80 173 105 966 65 92 32 41 72 74 4 36 94 67 158 10 88 142 45 126 2 86 118 73 79 121148 95 70 51 53 21 115 135 25 168 11 136 18 138 134 119 146 0 97 22 16540 19 60 46 14 49 139 58 101 39 116 127 30 98 50 107 35 62}

In accordance with another aspect of the present invention, there isprovided a bit interleaving method, including storing an LDPC codewordhaving a length of 64800 and a code rate of 7/15; generating aninterleaved codeword by interleaving the LDPC codeword on a bit groupbasis corresponding to the parallel factor of the LDPC codeword; andoutputting the interleaved codeword to a modulator for QPSK modulation.

In accordance with still another aspect of the present invention, thereis provided a BICM device, including an error-correction coderconfigured to output an LDPC codeword having a length of 64800 and acode rate of 7/15; a bit interleaver configured to interleave the LDPCcodeword on a bit group basis corresponding to the parallel factor ofthe LDPC codeword and output the interleaved codeword; and a modulatorconfigured to perform QPSK modulation on the interleaved codeword.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a block diagram illustrating a broadcast signal transmissionand reception system according to an embodiment of the presentinvention;

FIG. 2 is an operation flowchart illustrating a broadcast signaltransmission and reception method according to an embodiment of thepresent invention;

FIG. 3 is a diagram illustrating the structure of a parity check matrix(PCM) corresponding to an LDPC code to according to an embodiment of thepresent invention;

FIG. 4 is a diagram illustrating the bit groups of an LDPC codewordhaving a length of 64800;

FIG. 5 is a diagram illustrating the bit groups of an LDPC codewordhaving a length of 16200;

FIG. 6 is a diagram illustrating interleaving that is performed on a bitgroup basis in accordance with an interleaving sequence;

FIG. 7 is a block diagram illustrating a bit interleaver according to anembodiment of the present invention; and

FIG. 8 is an operation flowchart illustrating a bit interleaving methodaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings. Repeated descriptions anddescriptions of well-known functions and configurations that have beendeemed to make the gist of the present invention unnecessarily obscurewill be omitted below. The embodiments of the present invention areintended to fully describe the present invention to persons havingordinary knowledge in the art to which the present invention pertains.Accordingly, the shapes, sizes, etc. of components in the drawings maybe exaggerated to make the description obvious.

Embodiments of the present invention will be described in detail belowwith reference to the accompanying drawings.

FIG. 1 is a block diagram illustrating a broadcast signal transmissionand reception system according to an embodiment of the presentinvention.

Referring to FIG. 1, it can be seen that a BICM device 10 and a BICMreception device 30 communicate with each other over a wireless channel20.

The BICM device 10 generates an n-bit codeword by encoding k informationbits 11 using an error-correction coder 13. In this case, theerror-correction coder 13 may be an LDPC coder or a Turbo coder.

The codeword is interleaved by a bit interleaver 14, and thus theinterleaved codeword is generated.

In this case, the interleaving may be performed on a bit group basis (bya unit of a bit group). In this case, the error-correction coder 13 maybe an LDPC coder having a length of 64800 and a code rate of 7/15. Acodeword having a length of 64800 may be divided into a total of 180 bitgroups. Each of the bit groups may include 360 bits, i.e., the parallelfactor of an LDPC codeword.

In this case, the interleaving may be performed on a bit group basis (bya unit of a bit group) in accordance with an interleaving sequence,which will be described later.

In this case, the bit interleaver 14 prevents the performance of errorcorrection code from being degraded by effectively distributing bursterrors occurring in a channel. In this case, the bit interleaver 14 maybe separately designed in accordance with the length and code rate ofthe error correction code and the modulation order.

The interleaved codeword is modulated by a modulator 15, and is thentransmitted via an antenna 17. In this case, the modulator 15 may be aquadrature phase shift keying (QPSK) modulator. In this case, themodulator 15 is based on a concept including a symbol mapping device. Inthis case, the modulator 15 may be a uniform modulator, such as aquadrature amplitude modulation (QAM) modulator, or a non-uniformmodulator.

The signal transmitted via the wireless channel 20 is received via theantenna 31 of the BICM reception device 30, and, in the BICM receptiondevice 30, is subjected to a process reverse to the process in the BICMdevice 10. That is, the received data is demodulated by a demodulator33, is deinterleaved by a bit deinterleaver 34, and is then decoded byan error correction decoder 35, thereby finally restoring theinformation bits.

It will be apparent to those skilled in the art that the above-describedtransmission and reception processes have been described within aminimum range required for a description of the features of the presentinvention and various processes required for data transmission may beadded.

FIG. 2 is an operation flowchart illustrating a broadcast signaltransmission and reception method according to an embodiment of thepresent invention.

Referring to FIG. 2, in the broadcast signal transmission and receptionmethod according to this embodiment of the present invention, input bits(information bits) are subjected to error-correction coding at stepS210.

That is, at step S210, an n-bit codeword is generated by encoding kinformation bits using the error-correction coder.

In this case, step S210 may be performed as in an LDPC encoding method,which will be described later.

Furthermore, in the broadcast signal transmission and reception method,an interleaved codeword is generated by interleaving the n-bit codewordon a bit group basis at step S220.

In this case, the n-bit codeword may be an LDPC codeword having a lengthof 64800 and a code rate of 7/15. The codeword having a length of 64800may be divided into a total of 180 bit groups. Each of the bit groupsmay include 360 bits corresponding to the parallel factors of an LDPCcodeword.

In this case, the interleaving may be performed on a bit group basis (bya unit of a bit group) in accordance with an interleaving sequence,which will be described later.

Furthermore, in the broadcast signal transmission and reception method,the encoded data is modulated at step S230.

That is, at step S230, the interleaved codeword is modulated using themodulator.

In this case, the modulator may be a QPSK modulator. In this case, themodulator is based on a concept including a symbol mapping device. Inthis case, the modulator may be a uniform modulator, such as a QAMmodulator, or a non-uniform modulator.

Furthermore, in the broadcast signal transmission and reception method,the modulated data is transmitted at step S240.

That is, at step S240, the modulated codeword is transmitted over thewireless channel via the antenna.

Furthermore, in the broadcast signal transmission and reception method,the received data is demodulated at step S250.

That is, at step S250, the signal transmitted over the wireless channelis received via the antenna of the receiver, and the received data isdemodulated using the demodulator.

Furthermore, in the broadcast signal transmission and reception method,the demodulated data is deinterleaved at step S260. In this case, thedeinterleaving of step S260 may be reverse to the operation of stepS220.

Furthermore, in the broadcast signal transmission and reception method,the deinterleaved codeword is subjected to error correction decoding atstep S270.

That is, at step S270, the information bits are finally restored byperforming error correction decoding using the error correction decoderof the receiver.

In this case, step S270 corresponds to a process reverse to that of anLDPC encoding method, which will be described later.

An LDPC code is known as a code very close to the Shannon limit for anadditive white Gaussian noise (AWGN) channel, and has the advantages ofasymptotically excellent performance and parallelizable decodingcompared to a turbo code.

Generally, an LDPC code is defined by a low-density parity check matrix(PCM) that is randomly generated. However, a randomly generated LDPCcode requires a large amount of memory to store a PCM, and requires alot of time to access memory. In order to overcome these problems, aquasi-cyclic LDPC (QC-LDPC) code has been proposed. A QC-LDPC code thatis composed of a zero matrix or a circulant permutation matrix (CPM) isdefined by a PCM that is expressed by the following Equation 1:

$\begin{matrix}{{H = \begin{bmatrix}J^{a_{11}} & J^{a_{12}} & \cdots & J^{a_{1n}} \\J^{a_{21}} & J^{a_{22}} & \cdots & J^{a_{2n}} \\\vdots & \vdots & \ddots & \vdots \\J^{a_{m\; 1}} & J^{a_{m\; 2}} & \cdots & J^{a_{m\; n}}\end{bmatrix}},{{{for}\mspace{14mu} a_{ij}} \in \left\{ {0,1,\ldots\mspace{11mu},{L - 1},\infty} \right\}}} & (1)\end{matrix}$

In this equation, J is a CPM having a size of L×L, and is given as thefollowing Equation 2. In the following description, L may be 360.

$\begin{matrix}{J_{L \times L} = \begin{bmatrix}0 & 1 & 0 & \cdots & 0 \\0 & 0 & 1 & \cdots & 0 \\\vdots & \vdots & \vdots & \ddots & \vdots \\0 & 0 & 0 & \cdots & 1 \\1 & 0 & 0 & \cdots & 0\end{bmatrix}} & (2)\end{matrix}$

Furthermore, J^(i) is obtained by shifting an L×L identity matrix I (J⁰)to the right i (0≤i<L) times, and J^(∞) is an L×L zero matrix.Accordingly, in the case of a QC-LDPC code, it is sufficient if onlyindex exponent i is stored in order to store J^(i), and thus the amountof memory required to store a PCM is considerably reduced.

FIG. 3 is a diagram illustrating the structure of a PCM corresponding toan LDPC code to according to an embodiment of the present invention.

Referring to FIG. 3, the sizes of matrices A and C are g×K and(N−K−g)×(K+g), respectively, and are composed of an L×L zero matrix anda CPM, respectively. Furthermore, matrix Z is a zero matrix having asize of g×(N−K−g), matrix D is an identity matrix having a size of(N−K−g)×(N−K−g), and matrix B is a dual diagonal matrix having a size ofg×g. In this case, the matrix B may be a matrix in which all elementsexcept elements along a diagonal line and neighboring elements below thediagonal line are 0, and may be defined as the following Equation 3:

$\begin{matrix}{B_{g \times g} = \begin{bmatrix}I_{L \times L} & 0 & 0 & \cdots & 0 & 0 & 0 \\I_{L \times L} & I_{L \times L} & 0 & \cdots & 0 & 0 & 0 \\0 & I_{L \times L} & I_{L \times L} & \vdots & 0 & 0 & 0 \\\vdots & \vdots & \vdots & \ddots & \vdots & \vdots & \vdots \\0 & 0 & 0 & \cdots & I_{L \times L} & I_{L \times L} & 0 \\0 & 0 & 0 & \cdots & 0 & I_{L \times L} & I_{L \times L}\end{bmatrix}} & (3)\end{matrix}$where I_(L×L) is an identity matrix having a size of L×L.

That is, the matrix B may be a bit-wise dual diagonal matrix, or may bea block-wise dual diagonal matrix having identity matrices as itsblocks, as indicated by Equation 3. The bit-wise dual diagonal matrix isdisclosed in detail in Korean Patent Application Publication No.2007-0058438, etc.

In particular, it will be apparent to those skilled in the art that whenthe matrix B is a bit-wise dual diagonal matrix, it is possible toperform conversion into a Quasi-cyclic form by applying row or columnpermutation to a PCM including the matrix B and having a structureillustrated in FIG. 3.

In this case, N is the length of a codeword, and K is the length ofinformation.

The present invention proposes a newly designed QC-LDPC code in whichthe code rate thereof is 7/15 and the length of a codeword is 64800, asillustrated in the following Table 1. That is, the present inventionproposes an LDPC code that is designed to receive information having alength of 30240 and generate an LDPC codeword having a length of 64800.

Table 1 illustrates the sizes of the matrices A, B, C, D and Z of theQC-LDPC code according to the present invention:

TABLE 1 Sizes Code rate Length A B C D Z 7/15 64800 1080 × 30240 1080 ×1080 33480 × 31320 33480 × 33480 1080 × 33480

The newly designed LDPC code may be represented in the form of asequence (progression), an equivalent relationship is establishedbetween the sequence and matrix (parity bit check matrix), and thesequence may be represented, as follows:

Sequence Table 1st row: 460 792 1007 4580 11452 13130 26882 27020 324392nd row: 35 472 1056 7154 12700 13326 13414 16828 19102 3rd row: 45 440772 4854 7863 26945 27684 28651 31875 4th row: 744 812 892 1509 901812925 14140 21357 25106 5th row: 271 474 761 4268 6706 9609 19701 1970724870 6th row: 223 477 662 1987 9247 18376 22148 24948 27694 7th row: 44379 786 8823 12322 14666 16377 28688 29924 8th row: 104 219 562 583219665 20615 21043 22759 32180 9th row: 41 43 870 7963 13718 14136 1721630470 33428 10th row: 592 744 887 4513 6192 18116 19482 25032 34095 11throw: 456 821 1078 7162 7443 8774 15567 17243 33085 12th row: 151 666 9776946 10358 11172 18129 19777 32234 13th row: 236 793 870 2001 6805 904713877 30131 34252 14th row: 297 698 772 3449 4204 11608 22950 2607127512 15th row: 202 428 474 3205 3726 6223 7708 20214 25283 16th row:139 719 915 1447 2938 11864 15932 21748 28598 17th row: 135 853 902 323918590 20579 30578 33374 34045 18th row: 9 13 971 11834 13642 17628 2166924741 30965 19th row: 344 531 730 1880 16895 17587 21901 28620 3195720th row: 7 192 380 3168 3729 5518 6827 20372 34168 21st row: 28 521 6814313 7465 14209 21501 23364 25980 22nd row: 269 393 898 3561 11066 1198517311 26127 30309 23rd row: 42 82 707 4880 4890 9818 23340 25959 3169524th row: 189 262 707 6573 14082 22259 24230 24390 24664 25th row: 383568 573 5498 13449 13990 16904 22629 34203 26th row: 585 596 820 24402488 21956 28261 28703 29591 27th row: 755 763 795 5636 16433 2171423452 31150 34545 28th row: 23 343 669 1159 3507 13096 17978 24241 3432129th row: 316 384 944 4872 8491 18913 21085 23198 24798 30th row: 64 314765 3706 7136 8634 14227 17127 23437 31st row: 220 693 899 8791 1241713487 18335 22126 27428 32nd row: 285 794 1045 8624 8801 9547 1916721894 32657 33rd row: 386 621 1045 1634 1882 3172 13686 16027 22448 34throw: 95 622 693 2827 7098 11452 14112 18831 31308 35th row: 446 813 9287976 8935 13146 27117 27766 33111 36th row: 89 138 241 3218 9283 2045831484 31538 34216 37th row: 277 420 704 9281 12576 12788 14496 1535720585 38th row: 141 643 758 4894 10264 15144 16357 22478 26461 39th row:17 108 160 13183 15424 17939 19276 23714 26655 40th row: 109 285 6081682 20223 21791 24615 29622 31983 41st row: 123 515 622 7037 1394615292 15606 16262 23742 42nd row: 264 565 923 6460 13622 13934 2318125475 26134 43rd row: 202 548 789 8003 10993 12478 16051 25114 2757944th row: 121 450 575 5972 10062 18693 21852 23874 28031 45th row: 507560 889 12064 13316 19629 21547 25461 28732 46th row: 664 786 1043 91379294 10163 23389 31436 34297 47th row: 45 830 907 10730 16541 2123230354 30605 31847 48th row: 203 507 1060 6971 12216 13321 17861 2267129825 49th row: 369 881 952 3035 12279 12775 17682 17805 34281 50th row:683 709 1032 3787 17623 24138 26775 31432 33626 51st row: 524 792 104212249 14765 18601 25811 32422 33163 52nd row: 137 639 688 7182 816910443 22530 24597 29039 53rd row: 159 643 749 16386 17401 24135 2842933468 33469 54th row: 107 481 555 7322 13234 19344 23498 26581 3137855th row: 249 389 523 3421 10150 17616 19085 20545 32069 56th row: 395738 1045 2415 3005 3820 19541 23543 31068 57th row: 27 293 703 1717 34608326 8501 10290 32625 58th row: 126 247 515 6031 9549 10643 22067 2949034450 59th row: 331 471 1007 3020 3922 7580 23358 28620 30946 60th row:222 542 1021 3291 3652 13130 16349 33009 34348 61st row: 532 719 10385891 7528 23252 25472 31395 31774 62nd row: 145 398 774 7816 13887 1493623708 31712 33160 63rd row: 88 536 600 1239 1887 12195 13782 16726 2799864th row: 151 269 585 1445 3178 3970 15568 20358 21051 65th row: 650 819865 15567 18546 25571 32038 33350 33620 66th row: 93 469 800 6059 1040512296 17515 21354 22231 67th row: 97 206 951 6161 16376 27022 2919230190 30665 68th row: 412 549 986 5833 10583 10766 24946 28878 3193769th row: 72 604 659 5267 12227 21714 32120 33472 33974 70th row: 25 902912 1137 2975 9642 11598 25919 28278 71st row: 420 976 1055 8473 1151220198 21662 25443 30119 72nd row: 1 24 932 6426 11899 13217 13935 1654829737 73rd row: 53 618 988 6280 7267 11676 13575 15532 25787 74th row:111 739 809 8133 12717 12741 20253 20608 27850 75th row: 120 683 94314496 15162 15440 18660 27543 32404 76th row: 600 754 1055 7873 967917351 27268 33508 77th row: 344 756 1054 7102 7193 22903 24720 2788378th row: 582 1003 1046 11344 23756 27497 27977 32853 79th row: 28 429509 11106 11767 12729 13100 31792 80th row: 131 555 907 5113 10259 1030020580 23029 81st row: 406 915 977 12244 20259 26616 27899 32228 82ndrow: 46 195 224 1229 4116 10263 13608 17830 83rd row: 19 819 953 79659998 13959 30580 30754 84th row: 164 1003 1032 12920 15975 16582 2262427357 85th row: 8433 11894 13531 17675 25889 31384 86th row: 3166 38138596 10368 25104 29584 87th row: 2466 8241 12424 13376 24837 32711

An LDPC code that is represented in the form of a sequence is beingwidely used in the DVB standard.

According to an embodiment of the present invention, an LDPC codepresented in the form of a sequence is encoded, as follows. It isassumed that there is an information block S=(s₀, s₁, . . . , s_(K−1))having an information size K. The LDPC encoder generates a codewordΛ=(λ₀, λ₁, λ₂, . . . , λ_(N−1)) having a size of N=K+M₁+M₂ using theinformation block S having a size K. In this case, M₁=g, and M₂=N−K−g.Furthermore, M₁ is the size of parity bits corresponding to the dualdiagonal matrix B, and M₂ is the size of parity bits corresponding tothe identity matrix D. The encoding process is performed, as follows:

Initialization:λ_(i) =s _(i) for i=0,1, . . . ,K−1p _(j)=0 for j=0,1, . . . ,M ₁ +M ₂−1  (4)

First information bit λ₀ is accumulated at parity bit addressesspecified in the 1st row of the sequence of the Sequence Table. Forexample, in an LDPC code having a length of 64800 and a code rate of7/15, an accumulation process is as follows:

-   -   p₄₆₀=p₄₆₀⊕λ₀ p₇₉₂=p₇₉₂⊕λ₀ p₁₀₀₇=p₁₀₀₇⊕λ₀ p₄₅₈₀=p₄₅₈₀⊕λ₀        p₁₁₄₅₂=p₁₁₄₅₂⊕λ₀ p₁₃₁₃₀=p₁₃₁₃₀⊕λ₀ p₂₆₈₈₂=p₂₆₈₈₂⊕λ₀        p₂₇₀₂₀=p₂₇₀₂₀⊕λ₀ p₃₂₄₃₉=p₃₂₄₃₉⊕λ₀        where the addition ⊕ occurs in GF(2).

The subsequent L−1 information bits, that is, λ_(m), m=1, 2, . . . ,L−1, are accumulated at parity bit addresses that are calculated by thefollowing Equation 5:(x+m×Q ₁)mod M ₁ if x<M ₁M ₁+{(x−M ₁ +m×Q ₂)mod M ₂} if x≥M ₁  (5)where x denotes the addresses of parity bits corresponding to the firstinformation bit λ₀, that is, the addresses of the parity bits specifiedin the first row of the sequence of the Sequence Table, Q₁=M₁/L,Q₂=M₂/L, and L=360. Furthermore, Q₁ and Q₂ are defined in the followingTable 2. For example, for an LDPC code having a length of 64800 and acode rate of 7/15, M₁=1080, Q₁=3, M₂=33480, Q₂=93 and L=360, and thefollowing operations are performed on the second bit λ₁ using Equation5:

-   -   p₄₆₃=p₄₆₃⊕λ₁ p₇₉₅=p₇₉₅⊕λ₁ p₁₀₁₀=p₁₀₁₀⊕λ₁ p₄₆₇₃=p₄₆₇₃⊕λ₁        p₁₁₅₄₅=p₁₁₅₄₅⊕λ₁ p₁₃₂₂₃=p₁₃₂₂₃⊕λ₁ p₂₆₉₇₅=p₂₆₉₇₅⊕λ₁        p₂₇₁₁₃=p₂₇₁₁₃⊕λ₁ p₃₂₅₃₂=p₃₂₅₃₂⊕λ₁

Table 2 illustrates the sizes of M₁, Q₁, M₂ and Q₂ of the designedQC-LDPC code:

TABLE 2 Sizes Code rate Length M₁ M₂ Q₁ Q₂ 7/15 64800 1080 33480 3 93

The addresses of parity bit accumulators for new 360 information bitsfrom λ_(L) to λ_(2L−1) are calculated and accumulated from Equation 5using the second row of the sequence.

In a similar manner, for all groups composed of new L information bits,the addresses of parity bit accumulators are calculated and accumulatedfrom Equation 5 using new rows of the sequence.

After all the information bits from λ₀ to λ_(K−1) have been exhausted,the operations of the following Equation 6 are sequentially performedfrom i=1:p _(i) =p _(i) ⊕p _(i−1) for i=0,1, . . . ,M ₁−1  (6)

Thereafter, when a parity interleaving operation, such as that of thefollowing Equation 7, is performed, parity bits corresponding to thedual diagonal matrix B are generated:λ_(K+L·t+s) =p _(Q) ₁ _(·s+t) for 0≤s<L, 0≤t<Q ₁  (7)

When the parity bits corresponding to the dual diagonal matrix B havebeen generated using K information bits λ₀, λ₁, . . . , λ_(K−1), paritybits corresponding to the identity matrix D are generated using the M₁generated parity bits λ_(K), λ_(K+1), . . . , λ_(K+M) ₁ ⁻¹.

For all groups composed of L information bits from λ_(K) to λ_(K+M) ₁⁻¹, the addresses of parity bit accumulators are calculated using thenew rows (starting with a row immediately subsequent to the last rowused when the parity bits corresponding to the dual diagonal matrix Bhave been generated) of the sequence and Equation 5, and relatedoperations are performed.

When a parity interleaving operation, such as that of the followingEquation 8, is performed after all the information bits from λ_(K) toλ_(K+M) ₁ ⁻¹ have been exhausted, parity bits corresponding to theidentity matrix D are generated:λ_(K+M) ₁ _(+L·t+s) =p _(M) ₁ _(+Q) ₂ _(·s+t) for 0≤s<L, 0≤t<Q ₂  (8)

FIG. 4 is a diagram illustrating the bit groups of an LDPC codewordhaving a length of 64800.

Referring to FIG. 4, it can be seen that an LDPC codeword having alength of 64800 is divided into 180 bit groups (a 0th group to a 179thgroup).

In this case, 360 may be the parallel factor (PF) of the LDPC codeword.That is, since the PF is 360, the LDPC codeword having a length of 64800is divided into 180 bit groups, as illustrated in FIG. 4, and each ofthe bit groups includes 360 bits.

FIG. 5 is a diagram illustrating the bit groups of an LDPC codewordhaving a length of 16200.

Referring to FIG. 5, it can be seen that an LDPC codeword having alength of 16200 is divided into 45 bit groups (a 0th group to a 44thgroup).

In this case, 360 may be the parallel factor (PF) of the LDPC codeword.That is, since the PF is 360, the LDPC codeword having a length of 16200is divided into 45 bit groups, as illustrated in FIG. 5, and each of thebit groups includes 360 bits.

FIG. 6 is a diagram illustrating interleaving that is performed on a bitgroup basis in accordance with an interleaving sequence.

Referring to FIG. 6, it can be seen that interleaving is performed bychanging the order of bit groups by a designed interleaving sequence.

For example, it is assumed that an interleaving sequence for an LDPCcodeword having a length of 16200 is as follows:interleaving sequence={24 34 15 11 2 28 17 25 5 38 19 13 6 39 1 14 33 3729 12 42 31 30 32 36 40 26 35 44 4 16 8 20 43 21 7 0 18 23 3 10 41 9 2722}

Then, the order of the bit groups of the LDPC codeword illustrated inFIG. 4 is changed into that illustrated in FIG. 6 by the interleavingsequence.

That is, it can be seen that each of the LDPC codeword 610 and theinterleaved codeword 620 includes 45 bit groups, and it can be also seenthat, by the interleaving sequence, the 24th bit group of the LDPCcodeword 610 is changed into the 0th bit group of the interleaved LDPCcodeword 620, the 34th bit group of the LDPC codeword 610 is changedinto the 1st bit group of the interleaved LDPC codeword 620, the 15thbit group of the LDPC codeword 610 is changed into the 2nd bit group ofthe interleaved LDPC codeword 620, and the 11st bit group of the LDPCcodeword 610 is changed into the 3rd bit group of the interleaved LDPCcodeword 620, and the 2nd bit group of the LDPC codeword 610 is changedinto the 4th bit group of the interleaved LDPC codeword 620.

An LDPC codeword (u₀, u₁, . . . , u_(N) _(ldpc) ⁻¹) having a length ofN_(ldpc) is divided into N_(group)=N_(ldpc)/360 bit groups, as inEquation 9 below:X _(j) ={u _(k)|360×j≤k<360×(j+1), 0≤k<N _(ldpc)} for 0≤j<N_(group)  (9)where X_(j) is an j-th bit group, and each X_(j) is composed of 360bits.

The LDPC codeword divided into the bit groups is interleaved, as inEquation 10 below:Y _(j) =X _(π(j)) 0≤j≤N _(group)  (10)where Y_(j) is an interleaved j-th bit group, and π(j) is a permutationorder for bit group-based interleaving (bit group-unit interleaving).The permutation order corresponds to the interleaving sequence ofEquation 11 below:interleaving sequence={152 172 113 167 100 163 159 144 114 47 161 125 9989 179 123 149 177 1 132 37 26 16 57 166 81 133 112 33 151 117 83 52 17885 124 143 28 59 130 31 157 170 44 61 102 155 111 153 55 54 176 17 68169 20 104 38 147 7 174 6 90 15 56 120 13 34 48 122 110 154 76 64 75 84162 77 103 156 128 150 87 27 42 3 23 96 171 145 91 24 78 5 69 175 8 29106 137 131 43 93 160 108 164 12 140 71 63 141 109 129 82 80 173 105 966 65 92 32 41 72 74 4 36 94 67 158 10 88 142 45 126 2 86 118 73 79 121148 95 70 51 53 21 115 135 25 168 11 136 18 138 134 119 146 0 97 22 16540 19 60 46 14 49 139 58 101 39 116 127 30 98 50 107 35 62}  (11)

That is, when each of the codeword and the interleaved codeword includes180 bit groups ranging from a 0th bit group to a 179th bit group, theinterleaving sequence of Equation 11 means that the 152nd bit group ofthe codeword becomes the 0th bit group of the interleaved codeword, the172nd bit group of the codeword becomes the 1st bit group of theinterleaved codeword, the 113rd bit group of the codeword becomes the2nd bit group of the interleaved codeword, the 167th bit group of thecodeword becomes the 3rd bit group of the interleaved codeword, . . . ,the 35th bit group of the codeword becomes the 178th bit group of theinterleaved codeword, and the 62nd bit group of the codeword becomes the179th bit group of the interleaved codeword.

In particular, the interleaving sequence of Equation 11 has beenoptimized for a case where QPSK modulation is employed and an LDPC coderhaving a length of 64800 and a code rate of 7/15 is used.

FIG. 7 is a block diagram illustrating a bit interleaver according to anembodiment of the present invention.

Referring to FIG. 7, the bit interleaver according to the presentembodiment includes memories 710 and 730 and a processor 720.

The memory 710 stores an LDPC codeword having a length of 64800 and acode rate of 7/15.

The processor 720 generates an interleaved codeword by interleaving theLDPC codeword on a bit group basis corresponding to the parallel factorof the LDPC codeword.

In this case, the parallel factor may be 360. In this case, each of thebit groups may include 360 bits.

In this case, the LDPC codeword may be divided into 180 bit groups, asin Equation 9.

In this case, the interleaving may be performed using Equation 10 usingpermutation order.

In this case, the permutation order may correspond to the interleavingsequence represented by Equation 11.

The memory 730 provides the interleaved codeword to a modulator for QPSKmodulation.

The memories 710 and 730 may correspond to various types of hardware forstoring a set of bits, and may correspond to a data structure, such asan array, a list, a stack, a queue or the like.

In this case, the memories 710 and 730 may not be physically separatedevices, but may correspond to different addresses of a physicallysingle device. That is, the memories 710 and 730 are not physicallydistinguished from each other, but are merely logically distinguishedfrom each other.

The error-correction coder 13 illustrated in FIG. 1 may be implementedin the same structure as in FIG. 7.

That is, the error-correction coder may include memories and aprocessor. In this case, the first memory is a memory that stores anLDPC codeword having a length of 64800 and a code rate of 7/15, and asecond memory is a memory that is initialized to 0.

The memories may correspond to λ_(i)(i=0, 1, . . . , N−1) and P_(j)(j=0,1, . . . , M₁+M₂−1), respectively.

The processor may generate an LDPC codeword corresponding to informationbits by performing accumulation with respect to the memory using asequence corresponding to a parity check matrix (PCM).

In this case, the accumulation may be performed at parity bit addressesthat are updated using the sequence of the above Sequence Table.

In this case, the LDPC codeword may include a systematic part λ₀, λ₁, .. . , λ_(K−1), corresponding to the information bits and having a lengthof 30240 (=K), a first parity part λ_(K), λ_(K+1), . . . , λ_(K+M) ₁ ⁻¹corresponding to a dual diagonal matrix included in the PCM and havinglength of 1080 (=M₁=g), and a second parity part λ_(K+M) ₁ , λ_(K+M) ₁₊₁, . . . , λ_(K+M) ₁ _(+M) ₂ ⁻¹ corresponding to an identity matrixincluded in the PCM and having a length of 33480 (=M₂.

In this case, the sequence may have a number of rows equal to the sum(30240/360+1080/360=87) of a value obtained by dividing the length ofthe systematic part, i.e., 30240, by a CPM size L corresponding to thePCM, i.e., 360, and a value obtained by dividing the length M₁ of thefirst parity part, i.e., 1080, by 360.

As described above, the sequence may be represented by the aboveSequence Table.

In this case, the second memory may have a size corresponding to the sumM₁+M₂ of the length M₁ of the first parity part and the length M₂ of thesecond parity part.

In this case, the parity bit addresses may be updated based on theresults of comparing each x of the previous parity bit addresses,specified in respective rows of the sequence, with the length M₁ of thefirst parity part.

That is, the parity bit addresses may be updated using Equation 5. Inthis case, x may be the previous parity bit addresses, m may be aninformation bit index that is an integer larger than 0 and smaller thanL, L may be the CPM size of the PCM, Q₁ may be M₁/L, M₁ may be the sizeof the first parity part, Q₂ may be M₂/L, and M₂ may be the size of thesecond parity part.

In this case, it may be possible to perform the accumulation whilerepeatedly changing the rows of the sequence by the CPM size L (=360) ofthe PCM, as described above.

In this case, the first parity part λ_(K), λ_(K+1), . . . , λ_(K+M) ₁ ⁻¹may be generated by performing parity interleaving using the firstmemory and the second memory, as described in conjunction with Equation7.

In this case, the second parity part λ_(K+M), λ_(K+M) ₁ ₊₁, . . . ,λ_(K+M) ₁ _(+M) ₂ ⁻¹ may be generated by performing parity interleavingusing the first memory and the second memory after generating the firstparity part λ_(K), λ_(K+1), . . . , λ_(K+M) ₁ ⁻¹ and then performing theaccumulation using the first parity part λ_(K), λ_(K+1), . . . , λ_(K+M)₁ ⁻¹ and the sequence, as described in conjunction with Equation 8.

FIG. 8 is an operation flowchart illustrating a bit interleaving methodaccording to an embodiment of the present invention.

Referring to FIG. 8, in the bit interleaving method according to thepresent embodiment, an LDPC codeword having a length of 64800 and a coderate of 7/15 is stored at step S810.

In this case, the LDPC codeword may be represented by (u₀, u₁, . . . ,u_(N) _(ldpc) ⁻¹) (where N_(ldpc) is 64800), and may be divided into 180bit groups each composed of 360 bits, as in Equation 9.

Furthermore, in the bit interleaving method according to the presentembodiment, an interleaved codeword is generated by interleaving theLDPC codeword on a bit group basis at step S820.

In this case, the size of the bit group may correspond to the parallelfactor of the LDPC codeword.

In this case, the interleaving may be performed using Equation 10 usingpermutation order.

In this case, the permutation order may correspond to the interleavingsequence represented by Equation 11.

In this case, the parallel factor may be 360, and each of the bit groupsmay include 360 bits.

In this case, the LDPC codeword may be divided into 180 bit groups, asin Equation 9.

Moreover, in the bit interleaving method according to the presentembodiment, the interleaved codeword is output to a modulator for QPSKmodulation at step 830.

In accordance with at least one embodiment of the present invention,there is provided an intra-BICM bit interleaver that can effectivelydistribute burst errors occurring in a broadcasting system channel.

In accordance with at least one embodiment of the present invention,there is provided a bit interleaver that is optimized for an LDPC coderhaving a length of 64800 and a code rate of 7/15 and a QPSK modulatorperforming QPSK modulation and, thus, can be applied to next-generationbroadcasting systems, such as ATSC 3.0.

Although the specific embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible without departing from the scope and spirit of the invention asdisclosed in the accompanying claims.

What is claimed is:
 1. An apparatus for transmitting a broadcast signal,the apparatus comprising: a first memory configured to store alow-density parity check (LDPC) codeword having a length of 64800 and acode rate of 7/15; a processor configured to generate an interleavedcodeword by interleaving the LDPC codeword on a bit group basis, thesize of the bit group corresponding to a parallel factor of the LDPCcodeword; a second memory configured to output the interleaved codeword;a modulator configured to perform quadrature phase shift keying (QPSK)modulation corresponding to the interleaved codeword to generate amodulated signal; and an antenna configured to broadcast a transmissionsignal corresponding to the modulated signal over a physical channel toa reception device, the broadcasted transmission signal being anelectromagnetic signal having a radio frequency, wherein theinterleaving is performed using the following equation using permutationorder:Y _(j) =X _(π(j)) 0≤j<N _(group) where X_(π(j)) is a π(j) bit group,Y_(j) is an interleaved j-th bit group, and π(j) is a permutation orderfor bit group-based interleaving, wherein the permutation ordercorresponds to an interleaving sequence, the interleaving sequence beingfor the LDPC codeword having the length of 64800 and the code rate of7/15 and being represented as follows:={152 172 113 167 100 163 159 144 114 47 161 125 99 89 179 123 149 177 1132 37 26 16 57 166 81 133 112 33 151 117 83 52 178 85 124 143 28 59 13031 157 170 44 61 102 155 111 153 55 54 176 17 68 169 20 104 38 147 7 1746 90 15 56 120 13 34 48 122 110 154 76 64 75 84 162 77 103 156 128 15087 27 42 3 23 96 171 145 91 24 78 5 69 175 8 29 106 137 131 43 93 160108 164 12 140 71 63 141 109 129 82 80 173 105 9 66 65 92 32 41 72 74 436 94 67 158 10 88 142 45 126 2 86 118 73 79 121 148 95 70 51 53 21 115135 25 168 11 136 18 138 134 119 146 0 97 22 165 40 19 60 46 14 49 13958 101 39 116 127 30 98 50 107 35 62}, and wherein the interleavedcodeword is interleaved by the interleaving sequence on the bit groupbasis before performing the quadrature phase shift keying (QPSK)modulation so as to distribute burst errors occurring in thetransmission signal transmitted over the physical channel.
 2. Theapparatus of claim 1, wherein the parallel factor is 360, and the bitgroup includes 360 bits.
 3. The apparatus of claim 2, wherein the LDPCcodeword is represented by (u₀, u₁, . . . , u_(N) _(ldpc−1) ) (whereN_(ldpc) is 64800), and is divided into 180 bit groups each including360 bits, as in the following equation:X _(j) ={u _(k)|360×j≤k<360×(j+1), 0≤k<N _(ldpc)} for 0≤j<N _(group)where X_(j) is an j-th bit group, N_(ldpc) is 64800, and N_(group) is180.